Laboratory scale microcosm studies were conducted using site specific groundwater and aquifer solids to assess the feasibility of stimulating indigenous microorganisms in-situ to biologically transform Trichloroethylene (TCE) and its lesser chlorinated daughter products dichloroethylene (DCE) and vinyl chloride (VC). Three different treatments were conducted to determine the best approach for biologically remediating TCE under site specific conditions: anaerobic reductive dechlorination, aerobic cometabolism and sequential anaerobic/aerobic stimulation. Studies were conducted in batch serum bottles containing aquifer solids, groundwater and a gas headspace. Long-term (302 days) TCE anaerobic reductive dechlorination studies compared lactate, benzoate and methanol as potential anaerobic substrates. Site characteristic sulfate concentrations in the microcosms averaged 1,297 mg/L and TCE was added to levels of 2.3 mg/L. Substrates were added at one and a half times the stoichiometric electron equivalent of sulfate. Nutrient addition and bioaugmentation were also studied. Both benzoate and lactate stimulated systems achieved complete sulfate-reduction and prolonged dechlorination of TCE to VC and ethylene. Dechlorination was initiated between 15 to 20 days following lactate utilization and sulfate-reduction in the presence of approximately 300 mg/L sulfate. Benzoate amended microcosms did not initiate dechlorination until 120 to 160 days following the complete removal of available sulfate. After 302 days of incubation lactate and benzoate amended microcosms completely transformed TCE to VC with 7 to 15% converted to ethylene. Re-additions of TCE into both systems resulted in its rapid transformation to VC. The dechlorination of VC to ethylene was very slow and appeared to be dependent on VC concentration. Hydrogen addition at 10����� and 10������ atmospheres had no effect on the transformation of VC. Rapid methanol utilization resulted in its nearly stoichiometric conversion to methane and carbon dioxide without significant sulfate-reduction or dechlorination occurring. Nutrient addition slightly enhanced dehalogenation with lactate but inhibited it with benzoate. Bioaugmentation with a TCE dechlorinating culture from a previous benzoate amended Point Mugu microcosm effectively decreased lag-times and increased overall dechlorination. Aerobic cometabolism studies evaluated methane, phenol and propane as cometabolic growth substrates. Methane and phenol amended microcosms were able to remove only 50 to 60% of the added TCE after four stimulations, while propane utilizers were unable to cometabolize any TCE. Primary substrate utilization lag-times of 4 to 5 days, 0 to 0.5 days and 40 to 45 days were observed for methane, phenol and propane, respectively. Cometabolism of VC was possible in the presence of methane. Complete removal of 210 ��g/L VC was achieved after 2 stimulations with methane under strictly aerobic conditions. Methane utilization and VC oxidation required nitrate addition, indicating that the system was nitrate limited. A sequential anaerobic/aerobic microcosm study failed to achieve methane utilization and VC transformation likely due to oxygen being utilized to re-oxidize reduced sulfate in the system. / Graduation date: 1999

This study evaluated the potential of the aerobic Mycobacterium strain JS6O to grow on a variety of organic acid substrates, and the possible effects an organic acid would have on the degradation rate of vinyl chloride (VC). A series of batch growth tests were designed to determine the time it took to consume the substrate and the overall increase in biomass. Strain JS6O was found capable of growth on acetate, propionate, and butyrate, but could not grow on formate or lactate. Acetate was chosen for further study because strain JS6O consumed acetate the most rapidly of all the organic acids tested, and acetate is a common product of fermentation reactions in the subsurface. Strain JS6O was confirmed to grow on both ethylene and vinyl chloride as the sole carbon and energy source. Comparatively, strain JS6O's rate of growth on VC is much slower than that of ethylene. With acetate as an augmenting growth substrate, ethylene and VC utilization rates increased by 30% and 48%, respectively. Since acetate and VC are often found together in contaminated chlorinated ethene plumes, this makes a strong case for natural attenuation of VC by strain JS6O. A series of kinetic tests were implemented to determine the K[subscript s] and k[subscript max] of strain JS6O for ethylene, VC, and c-DCE. The K[subscript s] and k[subscript max] for ethylene determined through NLSR methods was similar to the values published in Coleman et al. (2002), supporting the maintenance of a pure culture throughout the experimental work. When strain JS6O was exposed to the isomers of DCE (trans-1,2-dichloroethylene (t-DCE), cis-1,2-dichloroethylene (c-DCE), and 1,1-dichloroethylene (1,1-DCE)) the cells were unable to grow on these compounds. However, when growing on acetate, strain JS6O cometabolized c-DCE and t-DCE, but not 1,1-DCE, with c-DCE transformed more rapidly than t-DCE. Transformation of c-DCE was also observed with growth on VC and ethylene. The presence of c-DCE was shown to partially inhibit VC degradation, but had no effect on ethylene degradation. The cometabolism results with acetate further indicate that strain JS6O is a good candidate for natural attenuation of multiple chlorinated ethenes in the subsurface. / Graduation date: 2006